Percutaneous transluminal angioplasty (PTA) is a well established procedure for the treatment of blockages in arteries. Blockages may occur from cholesterol buildup on the artery wall which may be in any stage from initial deposit through aged lesions. Arteries can also become blocked due to formation of thrombus.
The most widely used form of PTA makes use of a dilation balloon catheter, which has an expandable or inflatable balloon member proximate its distal end. The catheter is inserted into the patient's vascular system and guided until the balloon at the distal end of the catheter is positioned across a stenosis or blockage. A fluid is then fed under pressure through an inflation lumen of the catheter to the balloon, which causes the balloon to expand outward, thereby opening the stenosis.
Another use for balloon catheters is the placement of stents, grafts or stent/graft composites. To put a stent into position, the stent is placed around the balloon, and the balloon advanced into position within a vessel. The balloon is then inflated, expanding the stent outward against the vessel wall and into the desired shape and size. The balloon is deflated, leaving the stent in place. Balloons having smooth surfaces sometimes have difficulty in achieving separation of the balloon surface from the stent during balloon deflation. The smooth balloon surface has the potential to stick to the stent or graft. Sticking is more of a problem with some materials, such as glassy PTFE, than others.
One important characteristic of a dilation balloon used for angioplasty or stent placement is its profile, which is determined by the outer diameter of the distal end portion of the catheter and the balloon cross section. The outer diameter of the dilation balloon, both before inflation, during insertion and after treatment upon deflation, affects the ease and ability of the dilation catheter to pass through a guide catheter, through small caliber or small lumen arteries, and across a tight lesion. It is desirable to have a catheter having a low profile when the balloon is initially inserted uninflated and after treatment upon deflation for ease in both insertion and withdrawal.
In order to reduce the outer diameter of the balloon in its pre-inflation condition, it is common to fold the balloon flat, resulting in two wings being formed. These two wings are sometimes brought together in some fashion so as to reduce the overall diameter of the deflated balloon. This is commonly done by installing a sleeve or balloon protector around the deflated balloon to bring the two wings together. After inflation during treatment, it is often difficult to return balloon wings to their pre-inflation configuration. This becomes a problem when the balloon does not return to a diameter small enough to fit within the guide catheter, or pass across a tight lesion in multi-site angioplasty.
After dilation, the balloon is deflated by pulling vacuum on the balloon, collapsing the balloon, often referred to as "pancaking", forming flat wings having edges at their outermost extent. A non-elastic balloon having inflated diameter D, will have a post-inflation pancaked flat cross section of about Pi*D, a significant increase. The presence of wings and edges can interfere with ease of retraction, both through a guide catheter and through a body vessel or through a deployed implant such as a stent or graft. A smaller profile upon deflation is more desirable than a larger profile because of the increased ease of retraction and decreased contact with vessel walls. Various approaches have been taken to reduce the profile of balloons prior to retraction as summarized below.
Campbell et al. (U.S. Pat. No. 5,478,319) disclose a balloon having four longitudinal ribs, providing for four smaller wings upon deflation rather than two larger wings.
Hilstead (U.S. Pat. No. 5,366,472) discloses a dilation catheter having an elastic sleeve to expand with the balloon and contain the balloon wings after deflation.
Tsukashima et al. (U.S. Pat. No. 5,350,361) disclose a balloon having three smaller wings upon deflation rather than two larger wings.
Many of the folding improvements result in deflated balloons still having flat wings, albeit smaller ones, and still having outwardly projecting wing edges. There remains a need for a catheter balloon with improved folding characteristics. There also remains a need for a catheter balloon having improved, non-stick characteristics for stent and graft placement.